Why is the stainless steel cup red? What is the reason why stainless steel cups turn red?

1. The discoloration of the stainless steel cup is due to air oxidation, and the slight oxidation is golden yellow. The heavier color may be deep red or blue. The main purpose of preventing oxidation is to reduce the temperature of the weld exposed to the air after it loses protection.

2, the change of the material in the cup, when the material inside is different, the depth of the color will change due to the change of refractive index.